From my experience, it will tend to use the wireless.
I have also found that you can go to the Advanced TCP/IP properties, and manually set Gateway Metrics for each connection, so it will use the one you specify. I can't remember whether it is a higher or lower number it will use first Best way is to change the values of both, and try transferring a file, and see which connection it is using (open up Task Manager and go to the Networking tab)
Confused